Pressure sensitive adhesives have for a long time been used for attaching medical devices, such as ostomy appliances, dressings (including wound dressings), wound drainage bandages, devices for collecting urine, orthoses and prostheses to the skin.
It has been reported that humans for short periods can sweat more than 20,000 g/m2/24 h, see Main, K., K. O, Nilsson, and N. E. Skakkebaek, 1991, Influence of sex and growth hormone deficiency on sweating, Scand. J. Clin. Lab Invest 51:475-480.
Thus, the moisture handling ability of skin contact adhesives, i.e. both the water absorption capacity and the moisture vapour transmission rate of the adhesive, is important.
Pressure sensitive adhesives with high water vapour transmission, which are suitable for skin contact use, have been described in WO 2005/032401. The pressure sensitive adhesive composition described in this patent application is the reaction product of a polypropylene oxide having at least two unsaturated end groups and a polysiloxane cross-linking agent comprising Si—H groups. This application suggests the incorporation of water-soluble polymer or absorptive polymers into the adhesive but there are no details or examples as regards the amount or kind of water-soluble polymer or absorptive polymer to be incorporated into the adhesive. Also there is no clear description of the effect of the addition of water-soluble polymers or absorptive polymers have on the adhesive.
In the polyalkyleneoxide polymer for the continuous phase of the adhesive according to the present invention, more than 90% w/w of the polyalkyleneoxide polymer consist of polymerized alkyleneoxide moieties having three or more carbon atoms and even though the polyalkyleneoxide is hydrophobic, it has very good moisture vapour transmission rate. Being hydrophobic, the polyalkyleneoxide used for the continuous phase of the adhesive according to the present invention have, as such, a low water absorption capacity.
Hydrocolloids has for a long time been added to pressure sensitive adhesives, such as adhesives based on thermoplastic elastomers, in order to impart wet tack and moisture absorbent properties to the adhesive.
However, it is well known that retention of moisture in hydrocolloid adhesives may cause changes in the adhesive, such as swelling, loss of cohesion, loss of adhesion, and erosion or disintegration of the adhesive.
Furthermore, addition of hydrocolloids to adhesives increases the moduli of the adhesive, making the adhesive less skin friendly, harder and less comfortable to wear.
It has now been found, that a surprisingly high increase in water vapour permeability and water absorption capacity may be achieved by adding an amount of water absorbent hydrophilic agent that does not compromise the softness and the erosion resistance of the adhesives of the invention.